La Colonia Formation

The La Colonia Formation is a geological formation found in Argentina. Its rock layers, or strata, date back to a very old time called the Late Cretaceous. Scientists have found many fossils there, including some from dinosaurs.

At first, people thought the rocks were from about 73 to 72 million years ago, a time called the Campanian. But later studies suggested they are probably from 72 to 66 million years ago, known as the Maastrichtian. In 2021, new research using special methods to study magnetic patterns and tiny plants in the rocks showed the age might be even more exact: between 69 and 64 million years old. This helps scientists understand more about life from that ancient time.

Description

The La Colonia Formation is made up of three different layers. The first layer is up to 16 metres (52 feet) thick and is made of conglomerate. The second layer is the thickest, more than 100 metres (330 feet), and contains siltstone, claystone, and sandstone. The third layer is less than 10 metres (33 feet) thick and is made of clay, likely from a coastal ocean environment.

Scientists have found many old plants in this area, including types that lived in water. Recent discoveries show a wider variety of plants, such as ferns, gymnosperms, and flowering plants. Some of these plants include leaves and fruits from a special group called Nelumbonaceae. During a time called the Maastrichtian, much of Patagonia, where the La Colonia Formation is located, was covered by water, possibly turning the land into scattered islands.

Fossil content

The La Colonia Formation in Argentina has many important fossils from the Late Cretaceous period. Scientists have discovered remains of different animals, including dinosaurs, mammals, and snakes.

Over 300 mammal specimens have been found here. Fossils of madtsoiids and maybe boids snakes have also been uncovered.

Turtles

Fish

Plesiosaurs

Dinosaurs

Ornithischians

Sauropods

Theropods

Mammals

Snakes

Turtles from the La Colonia Formation
Genus	Species	Location	Stratigraphic position	Material	Images
Calvarichelys	C. coloniensis	Norte de Cerro Bayo 2	Middle levels	Skull and lower jaw; postcranial remains
Patagoniaemys	P. gasparinae	Buitre Chico in and around Norte de Cerro Bayo 2 Cerro Bosta		"skull fragments and several postcranial elements including a nearly complete vertebral column."
Yaminuechelys	aff.Y. gasparinii	Norte de Cerro Bayo 1 Norte de Cerro Bayo 2 Cerro Bosta		"Three specimens formed only by postcranial remains (mainly shell fragments)"
	Y. sulcipeculiaris

Plesiosaurs from the La Colonia Formation
Genus	Species	Location	Material	Images
Chubutinectes	C. carmeloi		Several vertebrae, ribs, partial pectoral and pelvic girdles, arm and leg bones, and gastroliths
Elasmosauridae indet.	Indeterminate	Norte de Cerro Bayo 1 Cerro Bosta	"three postcranial specimens that preserve cervical, dorsal and caudal vertebrae, ribs and gastroliths and three vertebrae without collection number"
Kawanectes	K. lafquenianum		"an incomplete mandible, nine cervical vertebrae, 14 dorsal vertebrae, three sacral vertebrae and five caudal vertebrae, and almost complete left fore limb, the isolated right humerus, both femora, ilia, pubes and the right ischium"
Sulcusuchus	S. erraini	Cerro Bosta	"part of skull and mandible"

Sauropods from the La Colonia Formation
Genus	Species	Location	Material	Images
Somphospondyli indet.	Indeterminate	Norte de Cerro Bayo 2	"Two fragmentary caudal vertebrae"
Titanomachya	T. gimenezi	Norte de Cerro Bayo 2	"Partial postcranial skeleton"

Theropods from the La Colonia Formation
Genus	Species	Location	Material	Images
Carnotaurus	C. sastrei	Pocho Sastre	"Nearly complete skeleton and skull"
Enantiornithes indet.	Indeterminate		A distal humerus
Koleken	K. inakayali	Norte de Cerro Bayo 1	"Quite complete and partially articulated skeleton"
Neornithes indet.	Indeterminate		A distal ulna
Theropoda indet.	Indeterminate	Norte de Cerro Bayo 2	"Metatarsal fragments of a single individual"